The present invention relates to semiconductor design technology, and more particularly, to technology for monitoring a fuse of a redundancy circuit among the internal circuits of a semiconductor memory device.
With the development of the high integration technology for semiconductor memory devices, the number of signal lines and memory cells included in one semiconductor memory device is increasing rapidly, and the linewidth of an internal circuit and the size of a memory cell are decreasing gradually due to a limited integration space, which increases the possibility of a defect in a memory cell of a semiconductor memory device. In spite of cell defects, semiconductor memory devices with a desired capacity can be produced with a high yield because a semiconductor memory device includes a redundancy circuit for repairing defective memory cells. The redundancy circuit includes redundancy memory cells and fuses for programming repair addresses corresponding to defective memory cells. Various tests are performed upon completion of a wafer process. A memory cell, which is determined to be defective but reparable, is replaced with a redundancy memory cell. That is, a programming operation is performed in an internal circuit to replace an address corresponding to a defective memory cell with an address of a redundancy memory cell. Thus, when the address corresponding to the defective memory cell is input, the defective memory cell is replaced with the redundancy memory cell, so that the memory device can perform a normal operation. A fuse programming method is used to program address information corresponding to a defective memory cell. A typical example of the fuse programming method is a laser blowing type (generally called ‘physical fuse type’) programming method that blows out a connected fuse using a laser beam. However, the physical fuse programming method using a laser beam is possible only in a wafer state before a semiconductor memory device is fabricated in a package. Thus, instead of the physical programming method, an electrical programming method is used to replace a defective memory cell with a redundancy memory cell in a package state. A fuse programmable in a package state is called an electrical fuse. An electrical fuse can be programmed by electrically changing the connection state of the electrical fuse. The electrical fuse can be subdivided into an anti-type fuse and a blowing-type fuse. When a programming operation is performed, the anti-type fuse changes from an open state to a short state whereas the blowing-type fuse changes from a short state to an open state. The electrical fuse is very high in terms of the efficiency in a package state because it aims at programming after a packaging process.
A physical fuse is programmed in a wafer state, whereas an electrical fuse is programmed in a package state. Therefore, the connection state of the programmed electrical fuse is difficult to monitor with the naked eye. In the related art, a package must be removed in order to monitor the connection state of an electrically programmed fuse. However, removing the package for a test process reduces the value of a finished product and the test efficiency.